Volume 226, Issue 2 -

We present an overview of numerical challenges in simulating electronic and transport properties of battery assemblies. Li diffusion paths within inorganic materials (olivine phosphates) are investigated using a dedicated accelerated molecular dynamics approach. The need of many-body electronic structure calculations is illustrated for the evaluation of intercalation potentials (LDA/GGA+ U ) and of transport properties (LDA+DMFT). Steps towards the improvement of silicon based anodic materials are shown. All in all, the framework of an ab initio simulation platform for materials for power storage is sketched.

We report about the use of different ionic liquids and catalyst materials in lithium-oxygen batteries. Different types of oxygen electrodes such as self-supporting oxygen electrodes and catalyst-coated separators were prepared by hot-pressing and spray-coating procedures, respectively. Porous carbon material such as Ketjen Black, binder material and different metal oxides were used to prepare the cathodes. Self-supporting oxygen electrodes and catalyst-coated separators consist of a carbon material loading of 10 and 1.5 mg/cm 2 , respectively. Electrolyte systems based on lithium bis-(trifluoromethylsulfonyl) imide (LiTFSI) in ionic liquids and lithium hexafluorophosphate (LiPF 6 ) in carbonate solvents were investigated in lithium-oxygen batteries. 1-butyl-1-methyl-pyrrolidinium bis-(trifluoromethylsulfonyl) imide and 1-butyl-1-methyl-pyrrolidinium tetracyanoborate as well as 1-ethyl-3-methyl-imidazolium bis-(trifluoromethylsulfonyl) imide, thi oisocyanat and dicyanamide were tested. The cell potential recorded for ionic liquids ranged from 2 to 2.5 V during the discharge process. At a current density of 0.1 mA/cm 2 geom discharge capacities were found to be higher for lithium-oxygen cells using imidazolium-based ionic liquids compared to pyrrolidinium-based ionic liquids. Discharge voltages between 2.7 and 2.8 V were observed for the carbonate-based solvents. The discharge potentials observed were independent of the metal oxide used, but the charge potentials were highly dependent on the catalyst materials employed. Good reversibility was obtained when the corresponding lithium-oxygen cells were cycled at 20–40% of their maximum capacity (mA h/g C).

One challenge in the use of metallic lithium in secondary lithium ion or lithium air batteries is the dendritic growth of lithium upon repeated cycling which might either lead to a short circuit or at least to an uneven current distribution and bad cycling stability. In the present paper we present our first results on the electrodeposition of lithium from an ionic liquid within the voids of a polystyrene opal structure on copper. For this purpose polystyrene spheres with an average diameter of about 600 nm were applied onto a copper sheet by a simple dipping process resulting in a layer thickness of about 10 μm. Lithium can be deposited within this polymer structure without damaging it and the subsequent dissolution of the polystyrene spheres delivers a macroporous lithium film, proving that a mechanically stable composite electrode is feasible.

Mixtures of Ionic Liquids as Possible Electrolytes for Lithium Ion Batteries Due to their unique properties like incombustibility, low vapor pressure, large electrochemical stability, wide liquid range and high thermal stability, ionic liquids have a great potential as components of electrolytes for lithium ion batteries. Lithium ion batteries with electrolytes on the basis of ionic liquids are safer than those with conventional electrolytes. Unfortunately, ionic liquids normally possess a higher viscosity and lower conductivities than conventional electrolytes. In order to decrease the viscosity and increase the conductivity of electrolytes based on ionic liquids, we prepared mixtures of ionic liquids. We could show that the viscosity of ionic liquids can be significantly reduced by using eutectic mixtures. Therefore, the conductivities of some mixtures were significantly higher than those of the pure ionic liquids. In addition, we could increase the conductivity by introducing functional groups in the side chain of the ionic liquids.

Asymmetric tetraalkylammonium salts of azolylborates were synthesized and studied with respect to their suitability as supporting electrolytes in electrochemical double layer capacitors. In contrast to current conducting salts used in this device, azolylborates exhibit an excellent stability towards thermal load and moisture. In addition to good conductivity and stability towards cathodic reduction we found certain limitations when more positive potentials were applied.

With the rising production of regenerative energy stronger focus on energy storage is necessary. One possibility to store electric energy is the use of battery technology. Especially high energy densities can be realized with metal-air batteries. Zinc-air batteries are known since more than 100 years, but have until now found use only in special markets. A well-known example is the battery for hearing aids. Many attempts have been undertaken to develop rechargeable zinc-based batteries, but only with limited success. Reasons for this fact and directions for future needs, applications and developments are discussed in the paper. Furthermore, first experiments for the use of ionic liquids as electrolytes in zinc-air-batteries are presented.

Solid state chemistry is already established as a conventional procedure for obtaining well-crystallized particles of LiFePO 4 with ordered structure. The disadvantages of this method still are the uncontrollable particle growth and agglomeration, long reaction time and moreover the cost of production. The advantages of using 1-Hexadecanol as an additive to create a reducing atmosphere and additionally as a carbon source for the solid state method the existence of iron in the oxidation state Fe 3+ can be prevented. The carbon coating can be controlled by the amount of the additive and the reaction conditions such as reaction time or reaction temperature. This modified synthesis cannot reduce the cost of energy but represents a simple variant to obtain both carbon coated LiFePO 4 with a specific conductivity up to 10 -2 S cm -1 and pure LiFePO 4 . The latter does not show any impurities as confirmed by Mös sbauer spectroscopy. The reaction time only takes three hours without any time-consuming preparations.

Lithium iron phosphate LiFePO 4 (LFP) is one of the promising new cathode materials for next generation lithium secondary batteries. Various synthesis strategies have been proposed to create LiFePO 4 particles with maximum efficiency. The spray pyrolysis is a suitable synthesis technique which allows to direct the particle formation in multiple ways. LiFePO 4 has successfully been synthesized by ultrasonic and nozzle spray pyrolysis. The obtained products were characterized by means of XRD and SEM analysis. Furthermore, the mechanism of the particle formation was investigated.